Paper bags having an inner polymeric lining film, have existed for a long time. U.S. Pat. No. 3,038,651 that was granted on 12 Jun. 1962, may be mentioned by way of example. Said patent describes a paper bag comprising a paper tubular outer layer having a window therein, and a cellophane tubular inner liner attached to the outer tubular layer by means of an adhesive. The window is closed only by the cellophane inner liner, which allows the product contained inside the bag to be seen. The bag has a perforation line in the vicinity of its sealed upper edge. The consumer opens the bag by tearing it away along the perforation line. If the product, for example cookies, is not consumed all at once after opening the bag, the consumer is recommended according to the cited patent to fold the remaining upper edge so as to tightly close the bag to reduce the possibility that the product becomes stale because of the contact with the air.
The technique of obtaining in the front of the bag by appropriate die cutting at least one window for direct vision of the product when the bag is, for example, exposed to the public on the shelf of a store, is already well known from the above mentioned U.S. Pat. No. 3,038,651 and widely spread in the distribution. All these bags have the same problem of not being able to be reliably sealed after the first opening and a partial consumption of the contents.
Also food bags, which are normally used to contain a sealed dry pasta, are very widespread in the distribution of goods; such food bags are constituted by a single polymeric generally transparent tubular layer, for example made of polypropylene, partially printed with the name, the characteristics of the contained product and more. The bag is heat sealed to the upper and lower edges. An easy open removable adhesive label is attached in many cases on the upper edges, that the consumer has to tear or cut to get to the contents. This adhesive label must be removed to open the bag and attached again to join the upper edges of the bag with a side of the latter: this allows the bag to be closed after removal of a part of its contents, the remaining part thereof being preserved from moisture and other external factors and prevented to spill out of the bag.
The use of an easy open adhesive label has not been hitherto possible to the bags having at least two layers, that are paper or similar material on the outside and an inside polymeric layer. In fact, if doing so, at the first removal of the adhesive label in order to open the bag, part of the paper that constitutes the outer layer of the bag would remain attached to the adhesive label. This would prevent the adhesive label to be attached again to the bag when one wants to close the bag after having partially taken out its contents. In the past, attempts have been made to solve this problem by using special glues suitable for allowing adhesion to normal papers or by using special papers such as silicone papers for obtaining a releasable adhesion of the two parts by normal glues of the adhesive labels. However it is seen that the use of special glues or papers in normal bags would have resulted in unacceptable increases in the cost of packaging of the products.
In this sense, the present invention makes possible to use adhesive labels with normal glues and a normal type of paper with a result of optimizing also industrial production costs.
Solving the above mentioned problem is important. Recently the use of bags that are only made of paper and intended to contain pasta being produced by traditional techniques has come back into favor. Paper printed with graphic elements that remind of the good old days makes more attractive the purchase and greater the reputation of the producers. Among other things, in the absence of the coating paper, the direct molding of the polymeric transparent layer creates an ineffective mixture between printing elements and contents of the bag.